Method and apparatus for capturing magnetic resonance image

ABSTRACT

When an RF pulse sequence is applied to obtain an MR signal, a pulse sequence and a blade pulse sequence that pass a center of a k-space are applied, and thus an over-sampling at the center of a k-space in a short scanning time may be enabled. Therefore, a method for capturing an MR image that is robust against a motion artifact includes applying a radio frequency (RF) pulse sequence; obtaining an MR signal in response to the applied RF pulse sequence; and generating an MR image from the obtained MR signal.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the priority from Korean Patent Application No.10-2012-0133941, filed on Nov. 23, 2012, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND

1. Field

Apparatuses and methods consistent with exemplary embodiments relate tocapturing a magnetic resonance (MR) image, by which dense data may beobtained at a center of a k-space.

2. Description of the Related Art

Magnetic resonance imaging (MRI) forms an image based on informationobtained by resonance after exposure of an atomic nucleus to a magneticfield. Resonance of the atomic nucleus is a phenomenon in which if aparticular high frequency energy is incident into the atomic nucleusmagnetized by an external magnetic field, the atomic nucleus in alow-energy state absorbs the high-frequency energy and thus is excitedto a high-energy state. The atomic nucleus has different resonancefrequencies according to its type, and resonance is affected by thestrength of the external magnetic field. In the human body, numerousatomic nuclei exist and generally, a hydrogen atomic nucleus is used tocapture an MR image of a patient.

An MRI system is non-invasive, has superior tissue contrast as comparedto a computed tomography (CT), and generates no artifact due to a bonetissue. Moreover, the MRI system may capture various cross-sections in adesired direction without changing a position of an object, and thus hasbeen widely used together with other image diagnostic apparatuses.

A diagnostic method based on MRI has various advantages, but when an MRIis performed, for example, to image a brain, a motion artifact generatedby movement of an object may cause degradation of the quality of the MRimage.

One approach to avoid the motion artifact is to eliminate an objectmotion. However, it is difficult to remove a cause for every motionartifact, as for example, breathing of a patient. When a high resolutionimage is required, such as for example, when imaging a brain, the motionartifact has a great influence upon the quality of the image, andstatically, 40% of the MR images of the brain have motion artifacts, and10% out of them need a rescan due to the motion artifacts.

Another approach is obtaining a large amount of effective captured datato improve a signal-to-noise ratio (SNR), or shortening a scan time.However, these two factors have a trade-off relationship, and therefore,a compromise for satisfying both of them at the same time is required.The scan time is directly proportional to the number of repetition times(TR), each of which refers to one period from a 90° pulse to the next90° pulse in a pulse sequence, and its own length of TR.

SUMMARY

Exemplary embodiments may address at least the above problems and/ordisadvantages and other disadvantages not described above. Also, theexemplary embodiments are not required to overcome the disadvantagesdescribed above, and an exemplary embodiment may not overcome any of theproblems described above.

One or more of exemplary embodiments provide a method and apparatus forcapturing an MR image, by which a scan time is shortened and an MRsignal, which is robust against a motion artifact, is obtained.

One or more of exemplary embodiments also provide a computer-readablerecording medium having recorded thereon a program for executing themethod of capturing an MR image on a computer.

According to an aspect of an exemplary embodiment, there is provided amethod of capturing a magnetic resonance image including applying aradio frequency (RF) pulse sequence, obtaining an MR signal in responseto the applied RF pulse sequence, and generating an MR image from theobtained MR signal, in which the applied pulse sequence includes atleast one spiral pulse sequence having a spiral trajectory on a k-spaceand at least one blade on the k-space.

According to an aspect of another exemplary embodiment, there isprovided an apparatus for capturing a magnetic resonance image includinga radio frequency (RF) transmitter for generating an RF pulse sequenceused to obtain an MR signal, a data processor for obtaining the MRsignal in response to an applied RF pulse sequence, and an imageprocessor for generating an MR image by processing the obtained MRsignal, in which the applied pulse sequence includes at least one spiralpulse sequence having a spiral trajectory on a k-space and at least oneblade on the k-space.

The at least one spiral pulse sequences may exist on a two-dimensional(2D) k-space and the trajectories of the at least one spiral pulsesequences may include a center of the 2D k-space.

The at least one blade may exist on the 2D k-space, and the trajectoriesof the at least one blade may intersect another pulse sequence at thecenter of the 2D k-space.

The applied pulse sequence may include two blades, and trajectories ofthe two blades may be orthogonal to each other.

The applied pulse sequence may include a plurality of spiral pulsesequences which exist on a three-dimensional (3D) k-space.

Respective trajectories of the plurality of spiral pulse sequences maybe perpendicular to one axis of the 3D k-space and may be parallel witheach other.

Respective trajectories of the plurality of spiral pulse sequences mayintersect each other with respect to one axis of the 3D k-space.

The at least one blade may exist on the 3D k-space, and the trajectoriesof the at least one blade may intersect each of the plurality of spiralpulse sequences at spiral centers.

The at least one blade may be generated according to at least one of anecho planar imaging (EPI) method, a fast spin echo (FSE) method, and aparallel imaging (PI) method.

The at least one blade may not have an equal interval.

According to an aspect of another exemplary embodiment, there isprovided a computer-readable recording medium having recorded thereon aprogram for executing the method of capturing an MR image on a computer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects will become more apparent by describingcertain exemplary embodiments, with reference to the accompanyingdrawings, in which:

FIG. 1 is a diagram of an MRI system;

FIG. 2 is a diagram illustrating an apparatus for capturing an MR signalin an MRI system;

FIG. 3 is a flowchart illustrating a method of capturing an MR imageaccording to an exemplary embodiment;

FIG. 4 is a diagram illustrating a blade trajectory of a 2D k-spaceusing a periodically rotated overlapping parallel lines with enhancedreconstruction (PROPELLER) technique;

FIG. 5 is a diagram illustrating a pulse trajectory of a 2D k-spaceaccording to an exemplary embodiment;

FIG. 6 is a diagram illustrating a pulse trajectory of a 3D k-spaceaccording to an exemplary embodiment;

FIGS. 7A and 7B illustrate a pulse trajectory of a 3D k-space accordingto another exemplary embodiment;

FIGS. 8A, 8B, 8C, and 8D illustrate generation of a blade and atrajectory according to another exemplary embodiment; and

FIG. 9 is a diagram illustrating a trajectory of a blade to which anauto calibration signal (ACS) line is added.

DETAILED DESCRIPTION

Certain exemplary embodiments are described in greater detail below withreference to the accompanying drawings.

In the following description, the same drawing reference numerals areused for the same elements even in different drawings. The mattersdefined in the description, such as detailed construction and elements,are provided to assist in a comprehensive understanding of exemplaryembodiments. Thus, it is apparent that exemplary embodiments can becarried out without those specifically defined matters. Also, well-knownfunctions or constructions are not described in detail since they wouldobscure exemplary embodiments with unnecessary detail.

The inventive concept is not limited to the exemplary embodimentsdescribed below and may be implemented in different forms.

Exemplary embodiments may be implemented by software or hardwarecomponents such as a field-programmable gate array (FPGA) or anapplication-specific integrated circuit (ASIC). The hardware componentmay include a storage medium capable of addressing, or may be configuredto be executed by one or more processors. Software component may includeobject-oriented software components, class components, and taskcomponents, and processes, functions, attributes, procedures,subroutines, segments of a program code, drivers, firmware, a microcode, a circuit, data, a database, data structures, tables, arrays, andvariables. Functions provided by different components may be combinedinto a smaller number of components or may be further separated intoadditional components.

FIG. 1 is a block diagram schematically illustrating the overallstructure of an MRI system 100 according to an exemplary embodiment. TheMRI system 100 may include a magnetic resonance image capturingapparatus 110, a magnetic resonance image processing apparatus 130, andan image display apparatus 150. The respective apparatuses of the MRIsystem 100 may be integrated rather than physically separated as shownin FIG. 1.

The magnetic resonance image capturing apparatus 110 receives input of acontrol signal for capturing an MR image, operates using the controlsignal, and obtains an MR signal used to generate an MR image from anobject 114 positioned in a magnet system 112 for output to the magneticresonance image processing apparatus 130. The object 114 is moved to abore 115 of the magnet system 112 on a cradle 116.

The magnetic resonance image processing apparatus 130 receives the MRsignal from the magnetic resonance image capturing apparatus 110,reconstructs the MR signal to generate the MR image of the object 114,and forwards the generated MR image to the image display apparatus 150.The magnetic resonance image processing apparatus 130 may include a userinterface for receiving control information from a user, an imageprocessor for reconstructing the MR signal to generate the MR image, astorage for storing the generated MR image and various information, andan input/output unit for connection with the magnetic resonance imagecapturing apparatus 110 and the image display apparatus 150.

The image display apparatus 150 receives the MR image generated by themagnetic resonance image processing apparatus 130 and displays the MRimage on a display unit.

FIG. 2 is a block diagram illustrating an MR image capturing apparatus210 for obtaining an MR signal in an MRI system 100 according to anexemplary embodiment. The MR image capturing apparatus 210 may include amagnet system 220, a gradient controller 230, a radio frequency (RF)transmitter 240, a data processor 250, and a controller 260. The magnetsystem 220 may include a main magnet 222, a gradient coil assembly 224,and an RF coil assembly 226. The MR image capturing apparatus 210 mayfurther include an amplifier for amplifying a signal and a low-passfilter (LPF) for noise processing.

According to an exemplary embodiment, the main magnet 222, the gradientcoil assembly 224, and the RF coil assembly 226 may have cylindricalshapes and may be arranged along the same central axis. As shown in FIG.2, the main magnet 222, the gradient coil assembly 224, and the RF coilassembly 226 are sequentially arranged in that order from outermost sideto the bore 115. The object 114 is located on the cradle 116 which ismoved to the bore 115 of the magnet system 220, such that a magneticfield and a high frequency may be applied to the object 114.

The main magnet 222 generates a static magnetic field B₀ in the bore 115of the magnet system 220. A direction of the static magnetic field B₀may be parallel or perpendicular to a body axis 270 of the object 114,i.e., to a longitudinal direction of the object 114. In the followingdescription, the static magnetic field B₀ is assumed to be a horizontalmagnetic field which is parallel to the body axis 270 of the object 114.

A hydrogen atomic nucleus has a magnetic moment, which may also bereferred to as a magnetic dipole moment, due to spinning movement. Whenan external magnetic field does not exist, the direction of the magneticmoment is random. When a hydrogen atom is situated in a static magneticfield, atomic nuclei become aligned in a static magnetic field directionto assume a low-energy state. For example, when a static magnetic fieldB₀ is applied to hydrogen atoms, a magnetic moment is arranged in adirection of the static magnetic field B₀.

Due to spinning movement of the hydrogen atomic nuclei, the magneticmoment is inclined by α, and nuclei perform precession about thedirection of the static magnetic field. Precession speed of atomicnuclei is determined by a precession frequency, i.e., Larmor frequencyF, which is a product of a gyromagnetic ratio γ and a strength B₀ of anexternally applied magnetic field:F=γB₀  (1)

where the gyromagnetic ratio γ may be a unique proportional constanthaving a value which differs according to an atomic nucleus.

A hydrogen atomic nucleus has a Larmor frequency of 42.58 Hz in amagnetic field of 1.0 T. If an electromagnetic wave corresponding tosuch a Larmor frequency is applied to an atomic nucleus, the atomicnucleus in a low-energy state transits to a high-energy state.

A main magnet which serves to generate a static magnetic field may be,for example, a permanent magnet, a room-temperature electromagnet, or asuperconducting electromagnet.

The gradient coil assembly 224 forms magnetic field gradients alongthree axes which are perpendicular to each other, such as coordinateaxes x, y, and z. One of the three axes may be a slice axis, another onemay be a frequency axis, and the other one may be a phase axis.

The slice axis may be set to have a direction which is inclined by aparticular angle with respect to the body axis 270. For example, z axismay be the slice axis, x axis may be the frequency axis, and y axis maybe the phase axis. Thus, the z axis is an axis extending along the bodyaxis 270.

When the static magnetic field B₀ is generated inside the bore 115,signals of tissues having similar characteristics are emitted at a time,making it difficult to identify which signal is emitted from whichposition. To solve this problem, a magnetic field gradient is generated.By using a magnetic field gradient in which the distribution of themagnetic field and a corresponding Larmor frequency linearly changespace by space, a hydrogen atomic nucleus at a particular position ofthe object, which corresponds to a region of interest (ROI), may beselectively resonated.

For example, a static magnetic field having a strength of 1.3 T through1.7 T may be formed in the bore. The magnetic field gradient may beformed in the direction of the body axis 270 of the object using thegradient coil assembly 224, to obtain an MR image of a cross-sectionwhich is perpendicular to the body axis, and a high frequency of theLarmor frequency corresponding to 1.5 T is applied to selectivelyresonate hydrogen atomic nuclei of that particular cross-section.Hydrogen atomic nuclei on a cross-section at another position do notgenerate resonance because of having a different Larmor frequency.

The gradient coil assembly 224 may form three magnetic field gradientsin the directions of x, y, and z axes of the object. To selectivelyexcite a particular cross-section which is perpendicular to the bodyaxis of the object, a magnetic field gradient is formed along the bodyaxis of the object, and in this case, a slice selection gradient isapplied. To obtain a 2D space information on the selected plane, afrequency encoded gradient and a phase encoded gradient are applied. Assuch, to form magnetic field gradients along the slice axis, thefrequency axis, and the phase axis, the gradient coil assembly 224 hasthree types of gradient coils.

The RF coil assembly 226 applies an RF pulse for exciting hydrogenatomic nuclei in the object and obtains electromagnetic waves generatedwhen the excited hydrogen atomic nuclei return to a stable state, i.e.,an MR signal. The RF coil assembly 226 according to an exemplaryembodiment may apply RF pulses of various types to the object, and mayapply a pulse sequence including a plurality of RF pulses to the object.

The gradient controller 230 is connected with the gradient coil assembly224, and outputs a signal to form the magnetic field gradient. Thegradient controller 230 includes driving circuits corresponding to threetypes of gradient coils for the slice axis, the frequency axis, and thephase axis. The RF transmitter 240 is connected with the RF coilassembly 226, and outputs an RF pulse and a signal related toapplication of the RF pulse to the RF coil assembly 226.

The data processor 250 is connected with the RF coil assembly 226,receives the MR signal from the RF coil assembly 226, and processes thereceived MR signal into digital data. The data processor 250 may includean amplifier for amplifying the received MR signal, a demodulator fordemodulating the amplitude of the MR signal, an analog-to-digitalconverter (ADC) for converting the demodulated analog signal into adigital format, and a storage for storing the MR signal converted intothe digital format. The MR signal converted into the digital format isforwarded to the magnetic resonance image processing apparatus 130, togenerate an MR image, for example, by an image processor 272.

The controller 260 controls the gradient controller 230, the RFtransmitter 240, and the data processor 250 to obtain an MR signal. Thecontroller 260 receives input of a control signal transmitted from theMR image processing apparatus to control the MR image capturingapparatus 210.

The controller 260 may further include a memory which may store aprogram for an operation of the controller 260, an RF pulse, and variousdata related to application of a pulse sequence. For example, the memorymay store information about a magnetic field gradient formed by thegradient coil assembly 224, a frequency value of an RF pulse based on astrength of a magnetic field, a duration time of an RF pulse related toa rotation angle of a magnetic moment of a hydrogen atomic nucleus, orinformation about the intensity of the RF pulse which is related to howfast the magnetic moment of the hydrogen atomic nucleus rotates. Thememory may also store tissue-based information for the time consumed torestore a state prior to application of the RF pulse from rotation ofthe magnetic moment of the hydrogen atomic nucleus due to the applied RFpulse, that is, the direction of the previously formed static magneticfield.

FIG. 3 is a flowchart illustrating a method of capturing an MR imageaccording to an exemplary embodiment. An object, which is positioned ona cradle, is moved to a bore of the magnet system 220. The entire objectmay be imaged or a specific portion of the object, for example, brain,may be imaged. When a driving signal is input to the RF transmitter 240from the controller 260, the RF coil assembly 226 receives input of anRF pulse sequence from the RF transmitter 240 and applies an RF pulsesequence to the object, in step 310.

The data processor 250 obtains an MR signal in response to the appliedRF pulse sequence, in step 320. For example, a spin echo (SE) method maybe used to obtain the MR signal. In an SE method, atomic nuclei startbeing de-phased from an instant when application of a 90° RF pulse isstopped, and in this state, a free induction decaying (FID) signal isemitted. Thereafter, various echo signals are obtained by using an RFcoil according to the application of a 180° RF pulse. Also, a pulsesequence may be generated by an FSE method, an inversion recovery (IR)method, a gradient echo (GE) method, a field echo (FE) method, an EPImethod, a PI method, and the like.

In step 330, the magnetic resonance image processing apparatus 130generates an MR image by performing post-processing of the MR signalobtained in step 320. The generated image is displayed on the imagedisplay apparatus 150.

A k-space is a data space of each cross-section, and by performingFourier transform on the k-space, a desired image may be obtained. Ifsizes of a phase encoded gradient and a frequency encoded gradient arechanged step-by-step after the RF pulse sequence is applied, then rawdata having various location information may be obtained. The raw datahas location information and tissue contrast information together, andthe k-space refers to a group of raw data which may form one image. Thecollected signal is stored in the k-space, and during each TR, eachslice identifies the location information based on the phase encodedgradient and the frequency encoded gradient.

When the MR image is a 2D image, it has a 2D k-space; if the MR image isa 3D image, it has a 3D k-space. Each axis of the k-space corresponds toa spatial frequency. A frequency component becomes a low-frequencycomponent toward the center of the k-space, so that the datacorresponding to the central region of a 3D k-space or a 2D k-space hasan effective meaning as an MR signal. Therefore, if the central regionof the k-space is denser, more effective data may be over-sampled andthus a high-quality MR image may be obtained.

However, due to a trade-off relationship between obtaining more data anda scan time as described above, if the central region of the k-spacebecomes excessively dense, the scan time increases, which may worseneffects due to the object motion, i.e., in the case of a child.

To obtain a high-resolution MR image or an MR image specified for adisease, a diffusion MRI method, a perfusion MRI method, or a functionalMRI method may be used.

The diffusion MRI method uses signal strength based on a diffusiondegree of a tissue by additionally using a pair of diffusion magneticfield gradients in addition to a general magnetic field gradient tomaximize weak signal reduction caused by diffusion. Thus, the diffusionMRI method images microscopic movement caused by diffusion of watermolecules in the tissue as a difference in diffusion coefficients,rather than using a direct blood vessel or blood stream inspection. Thediffusion MRI method may include two types: a diffusion weighted image(DWI) and a diffusion tensor image (DTI). The DWI allows observation ofmovement of micro water molecules, and the DTI allows analysis of nervefibers connecting two different tissues and movement of water molecules.A main application field of the diffusion MRI method is acute ischemicstroke (AIS), and the diffusion MRI method plays an important role,especially, in acute stroke.

The perfusion MRI method is an MRI technique which uses informationabout a blood volume per time of capillary flow, which is a blood streamflowing through a capillary to supply oxygen and nutrients toneighboring tissues. For this method, a first-pass method usingparamagnetic contrast media is mainly used, and the first-pass method iseasy to carry out and has a short scan time, but needs complexpost-processing and is prone to an error. A main application field ofthe perfusion MRI method is acute ischemic stroke (AIS) and braintumors, and the perfusion MRI method is mainly used to evaluatevascularity of tumors.

The functional MRI method uses a physiological phenomenon in which if abrain neural activity of a particular brain portion is accelerated, thenbrain blood stream and metabolism of that brain portion are locallyincreased, based on a fact that the brain performs a particular functionfor each brain portion. When compared to positron emission tomography(PET), the functional MRI method has superior space and timeresolutions, and does not need injection of a radioactive isotope andthus may be repetitively carried out. The functional MRI method hasevolved to a stage of imaging a cognitive function including a languagefunction from primary visual cortex and motor cortex images. Research isnow being conducted on sensorimotor functions or influences of medicinesupon brain functions.

FIG. 4 is a diagram illustrating a blade or a strip trajectory of a 2Dk-space using a PROPELLER technique. The blade has a linear trajectoryin which Cartesian pulse sequences corresponding to phase encoded linesare arranged in parallel with each other, having a predetermined length.The quality of an MR image may vary with the number of phase encodedlines which form the blade and an interval between the phase encodedlines which form the blade.

The PROPELLER technique fills the 2D k-space while rotating the bladeabout the origin at an angle. Since the central portion of the k-spaceis over-sampled, robustness against a structural motion artifact may beachieved and motion artifacts may be reduced or substantiallyeliminated, such that a better quality MR image may be obtained.However, according to the PROPELLER technique, when compared to othermethods using Cartesian pulses, the amount of k-space data is two orthree times greater and, correspondingly, a scan time is increased. Asshown in FIG. 4, eleven TRs are applied, and an increase in TRs causesan increase in a scan time. The TR for obtaining a complete MR image mayvary with the number of phase encoded lines of the blade and an intervalbetween the phase encoded lines. An increase in a scan time may becomegreater in 3D MR imaging.

FIG. 5 is a diagram illustrating a pulse trajectory of a 2D k-spaceaccording to an exemplary embodiment. In FIG. 5, there exists one spiralpulse sequence 510 having one spiral trajectory in a 2D k-space and twoblades 520 and 530 in the k-space.

In an exemplary embodiment shown in FIG. 5, the blades 520 and 530 areorthogonal to each other at the center of the spiral pulse sequence 510,such that the 2D k-space center may obtain a denser data sample than theother regions and thus an MR signal which is robust against a motionartifact may be obtained. In an exemplary embodiment of FIG. 5, the RFsequence is applied only three times, and only three TRs are needed,reducing a scan time and reducing an influence of a motion artifact inan MR image, and thereby reducing a negative influence of a specificabsorption rate (SAR) upon a human body. As mentioned previously, thescan time is proportional to the number TRs and a TR repetition period.

As shown, the blades 520, 530 are orthogonal to each other, but anintersecting angle between the blades may vary. Also, an exemplaryembodiment may include three or more blades and/or two or more spiralpulse sequences.

FIG. 6 is a diagram illustrating a pulse trajectory of a 3D k-spaceaccording to an exemplary embodiment. In an exemplary embodiment shownin FIG. 6, the pulse trajectory of the 3D k-space is structured suchthat pulse trajectories 540, 542, 546, 548, 550, 552, and 554 areperpendicular to an axis 556 of the 3D k-space and stacked in parallelwith each other. To reduce the number of TRs and the scan time, blades560, 561 may intersect each other on the spiral pulse trajectories 546,548, and 550 located near the center 562 of the 3D k-space, i.e., in acentral region of the k-space. The blades may only partially intersectthe spiral trajectories 542, 552 which are located further from thecenter 562 of the 3D k-space and may be omitted on the spiral pulsetrajectories 540, 554 which are located furthest from the center 562 ofthe 3D k-space.

FIG. 7A is a diagram illustrating a pulse trajectory of a 3D k-spaceaccording to another exemplary embodiment. In an exemplary embodiment ofFIG. 7A, the pulse trajectory of the 3D k-space is structured such thatthe pulse trajectories 570, 572, etc., intersect one another along anaxis 556 of the 3D k-space so that an angle is formed between the planesof the adjacent pulse trajectories. In a 2D k-space shown in FIG. 7B,two blades 574, 576 intersect each other and the pulse trajectory 570,as an example.

In the exemplary embodiments shown in FIGS. 6 and 7, an intersectingangle between blades may vary, and three or more blades may be includedfor each spiral pulse sequence or different numbers of blades may beincluded. Also, not all of the pulse trajectories shown in FIG. 7A maybe intersected by the blades.

FIGS. 8A, 8B, 8C, and 8D are diagrams illustrating generation of a bladeand a trajectory according to another exemplary embodiment. An FSEmethod of FIG. 8C applies a 90° RF pulse to obtain a plurality ofechoes, and applies a 180° RF pulse several times after reception of anFID signal. In this case, a different phase encoded gradient is appliedeach time before each echo is obtained, and after the echo is obtained,the phase encoded gradient is applied to the opposite side, therebyobtaining several frequency converted data in one TR. The FSE method mayperform scanning within a shorter time than an SE method, and thus theFSE method may efficiently obtain data while reducing an artifact.

An EPI method of FIGS. 8A and 8B is an ultrahigh-speed image capturingmethod capable of obtaining data by exciting a spin with one RF pulsethrough high-speed vibration of a magnetic field gradient. The EPImethod is one of the fastest functional MRI methods, and is used to scanbrain activities related to a change in a blood stream.

A PI method of FIG. 8D is an MRI method which reduces a scan time byreducing the number of times of magnetic field gradient encoding using adifference between sensitivities of different RF coils. Morespecifically, the PI method is implemented by recording an image whileunder-sampling a k-space at a plurality of RF coils. Through theunder-sampling, a scan time may be reduced, and through the use of theplurality of RF coils, imaging of a region out of an FOV, which may becaused by under-sampling, that is, an aliasing artifact may be reduced.

FIG. 9 is a diagram illustrating a trajectory of a blade to which an ACSline is added. The PI method uses an RF coil array, and anauto-calibrating technique may be applied such that k-space data may beadded by a linear combination of measured data. By adding an ACS line tothe central portion of a blade using the auto-calibrating technique, adenser data sample may be obtained at the central portion of thek-space. Therefore, in practice, similar data quality may be obtainedwith a smaller number of lines.

As is apparent from the foregoing description, when an RF pulse sequencefor obtaining an MR signal is applied, a spiral pulse sequence and ablade pulse sequence which pass the center of the k-space are applied,thereby reducing a scan time and generating an MR image which is robustagainst a motion artifact.

Terms used in the specification and claims should not be limited tocommon or lexical meanings and should be construed as meanings andconcepts suitable for the technical spirit of the present inventionbased on a principle that the inventor can define the concept of a termin order to describe his/her invention in the best way.

The foregoing exemplary embodiments and advantages are merely exemplaryand are not to be construed as limiting. The present teaching can bereadily applied to other types of apparatuses. Also, the description ofthe exemplary embodiments is intended to be illustrative, and not tolimit the scope of the claims, and many alternatives, modifications, andvariations will be apparent to those skilled in the art.

What is claimed is:
 1. A method of capturing a magnetic resonance (MR)image, the method comprising: applying a radio frequency (RF) pulsesequence; obtaining an MR signal in response to the applied RF pulsesequence; and generating an MR image from the obtained MR signal,wherein the applied RF pulse sequence comprises a spiral pulse sequencehaving a spiral trajectory centered on a k-space and a first blade and asecond blade intersecting one another and a spiral trajectory on thek-space, and each of the first blade and the second blade comprises atleast one parallel trajectory.
 2. The method of claim 1, wherein thespiral trajectory of the spiral pulse sequence spirals around a centerof a two-dimensional (2D) k-space.
 3. The method of claim 2, wherein atrajectory of the first blade intersects a trajectory of the secondblade near the center of the 2D k-space.
 4. The method of claim 3,wherein the trajectories of the first blade and the second blade areorthogonal to each other.
 5. The method of claim 1, wherein the appliedRF pulse sequence comprises a plurality of spiral pulse sequences in athree-dimensional (3D) k-space.
 6. The method of claim 5, whereinrespective trajectories of the plurality of spiral pulse sequences areperpendicular to one axis of the 3D k-space and are parallel with eachother.
 7. The method of claim 5, wherein respective trajectories of theplurality of spiral pulse sequences intersect each other at one axis ofthe 3D k-space.
 8. The method of claim 5, wherein a trajectory of thefirst blade intersects with each of the plurality of spiral pulsesequences at spiral centers, in the 3D k-space.
 9. The method of claim1, wherein the first blade is generated according to at least one of anecho planar imaging (EPI) method, a fast spin echo (FSE) method, and aparallel imaging (PI) method.
 10. The method of claim 1, wherein gapsbetween lines of the first blade are different from one another.
 11. Anon-transitory computer-readable recording medium having recordedthereon a program for executing the method of claim 1 by a computer. 12.The method of claim 1, wherein the spiral trajectory comprises a singlespiral which spirals through 360 degrees of a two-dimensional (2D)k-space.
 13. An apparatus for capturing a magnetic resonance (MR) image,the apparatus comprising: a radio frequency (RF) transmitter whichtransmits an RF pulse sequence; a data processor which obtains the MRsignal in response to an applied RF pulse sequence; and an imageprocessor which generates an MR image by processing the obtained MRsignal, wherein the applied RF pulse sequence comprises a spiral pulsesequence having a spiral trajectory centered on a k-space and a firstblade and a second blade intersecting one another and a spiraltrajectory on the k-space, and each of the first blade and the secondblade comprises at least one parallel trajectory.
 14. The apparatus ofclaim 13, wherein the spiral trajectory of the spiral pulse sequencespirals around a center of a two-dimensional (2D) k-space.
 15. Theapparatus of claim 14, wherein a trajectory of the first bladeintersects a trajectory of the second blade near the center of the 2Dk-space.
 16. The apparatus of claim 15, wherein the trajectories of thefirst blade and the second blade are orthogonal to each other.
 17. Theapparatus of claim 13, wherein the applied RF pulse sequence comprises aplurality of spiral pulse sequences in a three-dimensional (3D) k-space.18. The apparatus of claim 17, wherein respective trajectories of theplurality of spiral pulse sequences are perpendicular to one axis of the3D k-space and are parallel with each other.
 19. The apparatus of claim17, wherein respective trajectories of the plurality of spiral pulsesequences intersect each other at one axis of the 3D k-space.
 20. Theapparatus of claim 17, wherein a trajectory of the first bladeintersects with each of the plurality of spiral pulse sequences atspiral centers, in the 3D k-space.
 21. The apparatus of claim 13,wherein the first blade is generated according to at least one of anecho planar imaging (EPI) method, a fast spin echo (FSE) method, and aparallel imaging (PI) method.
 22. The apparatus of claim 13, whereingaps between lines of the first blade are different from one another.23. A magnetic resonance imaging (MRI) method comprising: generating aradio frequency (RF) pulse sequence comprising a spiral sequence with aspiral trajectory centered on a two-dimensional (2D) k-space and a firstblade and a second blade intersecting one another and the spiraltrajectory near a center of the 2D k-space; collecting MR signals inresponse to applying the RF pulse sequence into an imaging region inwhich an object is disposed; reconstructing an MR image from the MRsignals; and displaying the MR image on a display, wherein each of thefirst blade and the second blade comprises at least one paralleltrajectory.
 24. The method of claim 23, wherein the RF pulse sequencecomprises a plurality of spiral pulse sequences in a three-dimensional(3D) k-space, a trajectory of each of the plurality of spiral pulsesequences spirals around a same axis of the 3D k-space, and a trajectoryof the first blade extends in a direction of the same axis of the 3Dk-space and intersects the trajectory of some or all of the plurality ofspiral pulse sequences near spiral origins.
 25. The method of claim 23,wherein the RF pulse sequence comprises a plurality of spiral pulsesequences and a plurality of the first blades, in a three-dimensional(3D) k-space, a trajectory of each of the plurality of spiral pulsesequences spirals around a same axis of the 3D k-space, and thetrajectory of each of the plurality of the first blades extends in adirection perpendicular to the same axis of the 3D k-space andintersects trajectories of some of the plurality of spiral pulsesequences near spiral origins.
 26. The method of claim 25, wherein theRF pulse sequence comprises a plurality of second blades in the 3Dk-space, and a trajectory of each of the plurality of the second bladesextends in a direction of the same axis of the 3D k-space and intersectsthe trajectory of each of the plurality of the first blades near thespiral origins.
 27. The method of claim 23, wherein the RF pulsesequence comprises a plurality of spiral pulse sequences and a pluralityof the first blades, in a three-dimensional (3D) k-space, a trajectoryof each of the plurality of spiral pulse sequences intersects a sameaxis of the 3D k-space, and a trajectory of each of the plurality of thefirst blades extends in a direction perpendicular to the same axis ofthe 3D k-space and intersects the trajectory of some of the plurality ofspiral pulse sequences near spiral origins.
 28. The method of claim 27,wherein the RF pulse sequence further comprises a plurality of secondblades in the 3D k-space, and the trajectory of each of the plurality ofthe second blades intersects the trajectory of each of the plurality ofthe first blades near the spiral origins.